mgcp_internal: LOGPENDP: ensure *endp is not NULL

In certain cases the endp can be NULL. LOGPENDP will dereference the
pointer to retreive the endpoint number.

Fixes: 8a893442a1e9 ("mgcp_internal: LOGPENDP: ensure *endp is not NULL")
Change-Id: Ie9b5ecf08f69533ccb2fbd7fbbb529105e0c922f
diff --git a/include/osmocom/mgcp/mgcp_internal.h b/include/osmocom/mgcp/mgcp_internal.h
index 24e28b4..82ff6c8 100644
--- a/include/osmocom/mgcp/mgcp_internal.h
+++ b/include/osmocom/mgcp/mgcp_internal.h
@@ -338,7 +338,7 @@
 
 #define LOGPENDP(endp, cat, level, fmt, args...) \
 LOGP(cat, level, "endpoint:0x%x " fmt, \
-     ENDPOINT_NUMBER(endp), \
+     endp ? ENDPOINT_NUMBER(endp) : -1, \
      ## args)
 
 #define LOGPCONN(conn, cat, level, fmt, args...) \